Method of centrifugally casting hollow spheres

ABSTRACT

A method of centrifugally casting hollow spheres in a separable mold. The mold is partially filled with molten material and clamped in position with its center of rotation at the intersection of the axes of rotation of a rotating platform mounted on a main drive shaft and a second drive shaft mounted parallel to the plane of the rotating platform and at right angles to the axis of the main drive shaft. The mold is rotated about these two axes of rotation and the molten material is gradually solidified under the influence of the centrifugal forces established to form a hollow sphere. The rotating platform is dynamically balanced initially and heat is applied to the mold from an external source while rotating. The drive shafts are driven by electric motors one of which is mounted on the rotating platform and supplied with electrical power with the aid of slip rings.

United States Patent Amado, Jr.

[ 51 Dec. 30, 1975 METHOD OF CENTRIFUGALLY CASTING HOLLOW SPHERES lnventor: Juan Jose Amado, ,Ir., Aptdo. 4241, Panama 5, R.P., Panama [22] Filed: Sept. 16, 1974 [21] Appl. No.: 506,443

Related 115. Application Data [62] Division of Ser. No. 412,614, Nov. 5, 1973, Pat. No.

[52] US. Cl. 164/114; 164/287; 164/292 [51] Int. Cl. B221) 13/00 [58] Field of Search 164/114, 115, 116, 84, 164/85, 286, 287, 289, 292; 425/429, 430, 435

[ 56] References Cited UNITED STATES PATENTS 2,946,092 7/1960 Yoder 164/289 X 3,703,348 11/1972 Pivar 425/435 X 3,707,613 12/1972 Ujile.......... 164/85 UX 3,734,665 5/1973 Guillard 425/429 X 3,778,215 11/1973 Starr et al..... 164/116 X 3,788,792 1/1974 Suzuki Q 425/429 3,799,729 3/1974 Hogen 425/430 X 3,825,395 7/1974 Pivar 425/435 Primary Examiner-Ronald .1. Shore Attorney, Agent, or FirmWarren N. Low; Richard P. Matthews 57] ABSTRACT A method of centrifugally casting hollow spheres in a separable mold. The mold is partially filled with molten material and clamped in position with its center of rotation at the intersection of the axes of rotation of a rotating platform mounted on a main drive shaft and a second drive shaft mounted parallel to the plane of the rotating platform and at right angles to the axis of the main drive shaft. The mold is rotated about these two axes of rotation and the molten material is gradually solidified under the influence of the centrifugal forces established to form a hollow sphere. The rotating platform is dynamically balanced initially and heat is applied to the mold from an external source while rotating. The drive shafts are driven by electric motors one of which is mounted on the rotating platform and supplied with electrical power with the aid of slip rings.

4 Claims, 9 Drawing Figures U.S. Patent Dec. 30, 1975 Sheet 1 of 4 r LJ US. Patent Dec. 30, 1975 Sheet 2 of4 3,929,182

US. Patent Dec. 30, 1975 Sheet 3 of4 3,929,182

U.S. Patent Dec. 30, 1975 Sheet4 0f4 3,929,182

METHOD OF CENTRIFUGALLY CASTING HOLLOW SPHERES This is a division of application Ser. No. 412,614, filed Nov. 5, 1973, now US. Pat. No. 3,856,452.

This invention relates to a method of casting hollow spheres and, more particularly, to such a method wherein a spherical article is formed from molten material by centrifugally casting about two mutually perpendicular axes of rotation.

Heretofore attempts have been made to produce spherical articles by centrifugal casting techniques in which primarily mechanical driving means have been employed. In general, these devices have been too bulky and cumbersome to produce the articles at a sufficiently low price to make the production economically feasible. The previously known designs have also been difficult to effect dynamic balancing of the apparatus which is necessary to achieve containers or articles possessing uniform wall thickness.

In accordance with the present invention, the foregoing disadvantages and shortcomings are effectively overcome in the utilization of an electrically driven centrifugal casting apparatus. A first or main drive shaft is suitably journaled in a stationary frame means and driven by a fixedly mounted electric motor. A vertically disposed wheel or rotating platform means is driven by this main drive shaft. The rotating platform means carries two electric motors which are disposed diametrically apart in order to facilitate dynamic balancing of the wheel or rotating platform.

The first of these motors is used to drive a second shaft which extends parallel to the plane of the wheel or rotating platform means. This shaft carries one of two clamping members which serve to rotate a mold partially filled with molten material about an axis perpendicular to the axis of the main drive shaft and in a common plane therewith.

The second of the motors carried by the wheel or rotating platform means is used to drive a jack screw means used to advance or retract a freely rotatable shaft in line with the second drive shaft powered by the previously described carried motor. The end of this freely rotatable shaft carries a pad or clamping member which cooperates with the previously described clamping member to hold the mold securely for rotation about the axis of the second shaft parallel to the plane of the rotating platform. With the aid of the advancing and retracting means, the mold is capable of being positioned with its center of rotation at the intersection of the axes of the main drive shaft and a second drive shaft.

In a modified form of the invention, both pads or clamping members are made retractable whereby the apparatus may be used to manufacture spherical articles of different sizes. In this modified form of the invention, it is possible to mount the electric motor used to rotate the mold about a vertical axis on the advancing and retracting mechanism itself.

In practicing the method of the present invention, the following steps may be practiced:

l. disposing a rotatable platform means for rotation by a first drive shaft about a first axis;

2. mounting a second drive shaft parallel to the plane of the rotatable platform for rotation about a second axis which is perpendicular to the first axis and in a common plane therewith;

3. providing a separable mold for the reception of molten material;

4. partially filling the separable mold with a molten material;

5. clamping the mold with its center of rotation at the intersection of the first and second mutually perpendicular axes;

6. rotating the mold about the two mutually perpendicular axes of rotation and gradually solidifying the molten material under the influence of the centrifugal rotating forces established to form a hollow sphere;

7. supplying heat to the mold from an external source while the mold is rotating;

8. dynamically balancing the rotatable platform means; and,

9. mounting an electric motor on the rotatable platform to drive the second drive shaft and supplying this electric motor with power from slip rings.

A principal use of the articles formed from the practice of the foregoing steps is to store liquids or gases. For example, methane or propane may be stored in containers formed from the articles made in accordance with this invention. In this connection, the article produced herein may be drilled to provide attachment of dispensing valves or the like and may be provided with a suitable base or stand and handle means, if desired, and as is well known in the art.

The inherent advantages and improvements of the present invention will become more readily apparent upon considering the following detailed description of the invention and by reference to the drawings in which:

FIG. 1 is a side elevational view of the present invention for clamping a separable spherical mold and rotating it about two independent axes;

FIG. 2 is an end elevational view as seen from the sectional line 22 of FIG. 1;

FIG. 3 is a fragmentary end elevational view, drawn to an enlarged scale, illustrating the retractable clamping means of FIG. 2 in its retracted position;

FIG. 4 is a fragmentary side elevational view similar to FIG. 1 illustrating the retractable clamping means in its retracted position;

FIG. 5 is a fragmentary plan view taken in horizontal cross section along line 5-5 of FIG. 4 illustrating the retractable clamping means;

FIG. 6 is a perspective view, partly schematic in nature, illustrating the rotating apparatus shown in FIGS. l5;

FIG. 7 is an exploded perspective view showing a separable sphere for receiving a molten material;

FIG. 8 is a schematic perspective view similar to FIG. 6 showing a modified means for retracting both the upper and lower clamping means, and,

FIG. 9 is a front elevational view of the modified retractable clamping means shown in FIG. 8.

Referring now more particularly to FIG. 1, there is illustrated a centrifugal casting apparatus indicated generally at 10. Apparatus 10 is suitably mounted on a base I2 having upright support members 14 extending therefrom. A main drive shaft extends horizontally and is supported by bearing supports 18 which in turn are mounted on a horizontal support 20. An electric motor 22 is stationarily mounted either to the frame or to another solid structure and rotates a pulley drive means indicated generally at 24 through a series of belts and pulleys and is connected to a gear reducing mechanism 26. The output shaft 16 of the gear reducing mechanism 26 is the main drive shaft 16 which has a hub 28 fixedly secured thereto. A wheel or rotating platform means indicated generally at 30 is suitably attached to hub 28. The wheel or rotating platform means 30 has a rim which is designated at 31.

Referring now to FIGS. 1 and 2, the wheel or rotating platform means 30 is provided with suitable mounting plate members 32 and 34 and sufficient struts or bracing members 36.

An electric motor 38 used to rotate the mold in a manner to be described hereinafter is secured to mounting plate 32 and drives a shaft 40 through the intermediary of a pulley drive means indicated generally at 42. Shaft 40 is parallel to the plane of the wheel or rotating platform means 30 and spaced therefrom. In addition, shaft 40 is perpendicular to the axis of the main drive shaft 16 and in a common plane therewith. Heat resistant bearings are provided at 44 and 46 for drive shaft 40 and a first clamping means 48 consisting of a flat pad is secured to the end of shaft 40 for purposes of rotating a mold as will be described in greater detail hereinafter.

Diametrically opposed to electric motor 38 is another electric motor 50 used to advance and retract a lower clamping means through the intermediary of a jack screw 52. The jack screw drives a T-shaped slide member 70 as seen in greater detail in FIG. which in turn carries heat resistant bearings 54 for a freely rotatable shaft 56. A clamping means 58 is attached to the end of the freely rotatable shaft 56 which is identical with the clamping means shown at 48. Shaft 56 is in line with shaft 40 whereby it may be driven along with a spherical mold indicated generally at 60 disposed in between the two clamping means 48 and 58.

The spherical mold 60 is illustrated in greater detail in FIG. 7 and is shown to comprise upper and lower halves 62, 64 and interfitting parts 66 and 68. Other forms of spherical molds may be used although it should be observed that in accordance with the present invention no internal core is used in the mold.

Referring now to FIGS. 3-5, it will be seen that the electric motor 50 is used to raise and lower the mold 60 into position through the intermediary ofjack screw 52 which carries the lower shaft 56 in suitable heat resistant bearings 54. FIGS. 3 and 4 illustrate the retracted position of the mold 60 in solid lines and the fully advanced position in phantom lines. The jack screw 52 carries a T-shaped slide member 70 which slides in a U-shaped slide guide means 72. The freely rotatable shaft 56 which is guided in heat resistant bearings 54 and onto which clamping means 58 is secured moves along with the advance or retraction of the T-shaped slide member 70.

Referring to FIGS. 1 and 4, electrical power from a source not shown is introduced by electrical leads 75 and 76 to slip rings 74 on shaft 16 and is transmitted to the rotating electric motors 38 and 50 on rotating platform means by means of electrical leads 77 and 78. For purposes of this invention, the use of slip rings in supplying power to a motor on a rotating device may be deemed to be conventional.

In order to prevent premature solidification of the molten material contained within spherical mold 60, especially during periods of acceleration and until a constant angular velocity is reached, heat is applied to the rotating spherical mold 60 by any suitable means such as by an oxy-acetylene torch 80 indicated schematically in FIG. 1. Heat may be supplied alternatively by a stationary induction coil that surrounds the mold but which does not rotate therewith. A control panel is indicated generally in phantom at 82 in FIG. 1.

The operation of the embodiment illustrated in FIGS. 1 through 4 will now be explained with some reference to the schematic representation in FIG. 6. With the lower shaft 56 and associated clamping means 58 in the retracted position illustrated in solid lines in FIGS. 3 and 4, mold 60 may be opened and a desired quantity of molten metal poured therein so as to partially fill spherical mold 60. The mold halves 62 and 64 are assembled and the electric motor 50 is actuated to drive jack screw 52 and advance shaft 56 and lower clamping means 58 until the spherical mold 60 assumes the position shown in phantom lines in FIGS. 3 and 4 and in the solid lines in FIGS. 1, 2 and 6. The entire rotating mechanism has previously thereto been dynamically balanced so that at this moment electric motor 20 may be actuated to rotate the rotating platform 30 by means of drive shaft 16. Concurrently therewith electric motor 38 receives its power from slip rings 74 and rotates shaft 40 about its axis and as indicated by the arrows in FIG. 6. Thus with rotating platform 30 rotating in the direction indicated by arrow 84 in FIG. 6 the main drive shaft 16 will rotate in the direction indicated by arrows 86. Similarly, electric motor 38 drives shaft 40 in a direction of rotation indicated by arrows 88 which is at right angles to and in a common plane with the axis of the rotating platform means 30 and main drive shaft I6. Heat is applied to spherical mold 60 by a hand-held oxy-acetylene torch or other suitable heating means to prevent premature solidification or freezing of the molten material within the mold.

For purposes of illustration, mold 60 is rotated from I00 to 300 r.p.m. approximately to be adjusted to the sphere diameter and the wheel or rotating platform 30 is rotated at from ISO to 350 r.p.m. approximately to be adjusted to the sphere diameter. Spheres actually produced on the device shown in FIGS. 1 through 5 were [4 inches in outer diameter but the same method can be used for making smaller or larger spheres. The limiting factor for the smaller spheres is the higher rotational speeds required. For larger spheres it is only a matter of making a larger machine as the rotational speed is lower.

Commutation should be controlled for any changes in mold speed during the operation. The bearing materials should be heat resistant. A cast iron mold material has been found to be satisfactory for centrifugally casting aluminum. For other metals having a higher melting temperature, a refractory mold within a steel shell is necessary.

For the particular example previously described of a 14 inch outer diameter sphere, a five horsepower mold motor with variable speed was employed and a fifteen horsepower wheel motor with fixed speed was employed. In addition to molten metal, other plastic materials that exist as liquid at the start of the forming operation may be employed.

Because vibration is a problem, the equipment has to be dynamically balanced with great care. By adjusting the mold speed and the wheel speed the thickness can be made more even or uniform throughout the surface of the spherical article. As has already been noted, the wheel speed and the mold speed must bear a relation to the diameter of the sphere, the larger the diameter the lower the angular or rotational speed.

In order to stop the mechanism, it is possible to employ a brake. However, it has been found to be satisfactory to increase the deceleration rate by reversing the magnetic field on the driving motor during short intervals.

Referring now to FIGS. 8 and 9, a modified form of the invention is illustrated wherein both clamping means 48 and 50 (FIG. 9) may be advanced or retracted. In this embodiment, not only is an electric motor 50 and jack screw 52 used to advance and retract the lower illustrated clamping means 58 but also an upper electric motor 50a and jack screw 52a are used to advance and retract upper clamping means 48. In this embodiment, it becomes possible to have electric motor 38 and associated pulley means 42 move with the advance and retraction of the upper clamping means 48. Therefore, it becomes possible to manufacture different sized spherical articles on the same apparatus. The method employed in FIGS. 8 and 9 is identical with that described previously with respect to FIGS. 1 through 6 after the mold has been clamped in position for rotation about two mutually perpendicular axes.

While presently preferred embodiments of the invention have been illustrated and described, it will be recognized that the invention may be otherwise variously embodied and practiced within the scope of the claims which follow.

I claim:

1. A method of centrigually casting hollow spheres from molten metal comprising the steps of a. disposing a rotatable platform means for rotation by a first drive shaft about a first axis,

b. mounting a second drive shaft parallel to the plane of said rotatable platform for rotation about a second axis which is perpendicular to said first axis and in a common plane therewith,

c. providing a pair of mold parts to form a separable mold for the reception of molten metal,

d. partially filling said separable mold with a molten metal,

e. clamping said mold with a pair of clamping members at least one of which may be advanced toward and away from said mold parts so as to clamp said mold with its center of rotation at the intersection of said first and second axes,

f. and rotating said mold about said two axes of rotation and gradually solidifying said molten metal under the influence of the centrifugal rotational forces established to form a hollow sphere.

2. A method of centrifugally casting hollow spheres from molten metal as defined in claim 1 including the additional step of supplying heat to said mold from an external source while said mold is rotating.

3. A method of centrifugally casting hollow spheres from molten metal as defined in claim 1 including the additional step of dynamically balancing said rotatable platform means 4. A method of centrifugally casting hollow spheres from molten metal as defined in claim 1 including the additional steps of mounting an electric motor on said rotatable platform to drive said second drive shaft and supplying said electric motor with power from slip rings. 

1. A method of centrigually casting hollow spheres from molten metal comprising the steps of a. disposing a rotatable platform means for rotation by a first drive shaft about a first axis, b. mounting a second drive shaft parallel to the plane of said rotatable platform for rotation about a second axis which is perpendicular to said first axis and in a common plane therewith, c. providing a pair of mold parts to form a separable mold for the reception of molten metal, d. partially filling said separable mold with a molten metal, e. clamping said mold with a pair of clamping members at least one of which may be advanced toward and away from said mold parts so as to clamp said mold with its center of rotation at the intersection of said first and second axes, f. and rotating said mold about said two axes of rotation and gradually solidifying said molten metal under the influence of the centrifugal rotational forces established to form a hollow sphere.
 2. A method of centrifugally casting hollow spheres from molten metal as defined in claim 1 including the additional step of supplying heat to said mold from an external source while said mold is rotating.
 3. A method of centrifugally casting hollow spheres from molten metal as defined in claim 1 including the additional step of dynamically balancing said rotatable platform means.
 4. A method of centrifugally casting hollow spheres from molten metal as defined in claim 1 including the additional steps of mounting an electric motor on said rotatable platform to drive said second drive shaft and supplying said electric motor with power from slip rings. 